Plating apparatus and method of manufacturing printed circuit board

ABSTRACT

A plating apparatus includes a plating tank. The plating tank contains a plating solution. A long-sized substrate is transported by transport rollers to pass through inside of the plating tank. Three or more bar-shaped anodes are provided in the plating tank to line up along the long-sized substrate. A surface area of each of the anodes arranged at both ends is smaller than a surface area of another anode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plating apparatus and a method of manufacturing a printed circuit board.

2. Description of the Background Art

In recent years, various types of electronic equipment employ printed circuit boards having improved density and reduced size. In manufacture of the printed circuit board, a seed layer that has previously been formed is subjected to electrolytic plating by a plating apparatus in a process of forming wiring traces, for example.

A plating apparatus disclosed in JP 2003-321796 A, for example, includes a plating tank containing a plating solution. An anode is placed in the plating tank. A long-sized substrate is transported into the plating tank through a slit formed on a side wall of the plating tank. In the state, a voltage is applied between the anode and a region of the long-sized substrate to be subjected to the electrolytic plating. This causes the long-sized substrate to be subjected to the electrolytic plating in the plating tank.

If an excessively large current flows through the anode, such a phenomenon as a rough surface (plating burn) may occur in a metal layer that is deposited by the electrolytic plating. Therefore, the current flowing through the anode needs to be adjusted so as not to exceed an upper limit of the current at which plating burn does not occur.

In some cases, a plurality of anodes are arranged to line up within the plating tank for the purpose of improving efficiency of plating. In the case, however, currents flowing through the plurality of anodes may vary. The currents flowing through all the anodes need to be adjusted so as not to exceed the upper limit of the current at which plating burn does not occur in order to prevent plating burn. This may result in significantly small currents flowing through a part of anodes. This inhibits the plating from being efficiently performed.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a plating apparatus capable of improving efficiency of plating while preventing plating burn, and a method of manufacturing a printed circuit board.

(1) According to one aspect of the present invention, a plating apparatus arranged to perform plating on a long-sized substrate includes a plating solution container arranged to contain a plating solution, a transporting unit arranged to transport the long-sized substrate in a length direction of the long-sized substrate through the plating solution container, three or more anodes placed in the plating solution container to line up along the long-sized substrate transported by the transporting unit, and a power feeding unit arranged to apply a voltage between the long-sized substrate and the three or more anodes such that the long-sized substrate acts as a cathode, wherein a surface area of each of the anodes, which are arranged at both ends, of the three or more anodes is smaller than a surface area of at least another anode.

In the plating apparatus, the long-sized substrate is transported in its length direction by the transporting unit through the plating solution container that contains the plating solution. The three or more anodes are placed in the plating solution container to line up along the direction in which the long-sized substrate is transported. In this state, the voltage is applied between the plurality of anodes and the long-sized substrate by the power feeding unit such that the long-sized substrate acts as the cathode.

Experiments and study conducted by the inventor show that when constant currents are supplied to the plurality of anodes arranged along the long-sized substrate, each of currents flowing from the anodes at the both ends to the long-sized substrate tends to be larger than a current flowing from the another anode to the long-sized substrate. Therefore, current density at each of portions of the long-sized substrate that are opposite to the anodes at the both ends is larger than current density at a portion of the long-sized substrate that is opposite to the another anode.

In the plating apparatus according to the one aspect of the present invention, the surface area of each of the anodes, which are arranged at the both ends, of the plurality of anodes is set smaller than the surface area of the at least another anode. In this case, a resistance value of each of the anodes arranged at the both ends is larger than a resistance value of the at least another anode. This suppresses the currents flowing from the anodes at the both ends to the long-sized substrate. Thus, each of the currents flowing from the anodes at the both ends to the long-sized substrate can be equal or close to the current flowing from the at least another anode to the long-sized substrate. Accordingly, the current density at each of the portions of the long-sized substrate that are opposite to the anodes at the both ends can be equal or close to the current density of the portion of the long-sized substrate that is opposite to the at least another anode. In this case, the constant currents supplied to the plurality of anodes are increased, thereby allowing the currents flowing from the anodes at the both ends to the long-sized substrate and the current flowing from the at least another anode to the long-sized substrate to be close to an upper limit of the current at which plating burn does not occur. As a result, efficiency of the plating performed on the long-sized substrate can be improved while plating burn is prevented.

(2) Each of the three or more anodes may be composed of a metal bar, and an area of the cross section of each of the anodes arranged at the both ends may be smaller than an area of the cross section of the at least another anode, and the cross sections of the anodes may be perpendicular to a length direction of the anodes.

In this case, the area of the cross section, which is perpendicular to the length direction, of the anode made of the metal bar is adjusted in manufacture of each anode, so that the surface area of each anode can be accurately adjusted. Accordingly, the area of the cross section, which is perpendicular to the length direction, of each of the anodes arranged at the both ends is made smaller than the area of the cross section, which is perpendicular to the length direction, of the at least another anode, so that each of the currents flowing from the anodes at the both ends to the long-sized substrate can be accurately equal or close to the current flowing from the at least another anode to the long-sized substrate.

(3) Each of the three or more anodes may include a plurality of metal balls, and a case in which the plurality of metal balls are accommodated, and the number of the metal balls in each of the anodes, which are arranged at the both ends, of the three or more anodes may be smaller than the number of the metal balls in the at least another anode.

In this case, the surface area of each anode can be easily adjusted by adjusting the number of metal balls of each anode. Accordingly, the number of metal balls in each of the anodes arranged at the both ends is made smaller than the number of metal balls in the at least another anode, so that each of the currents flowing from the anodes at the both ends to the long-sized substrate can be easily equal or close to the current flowing from the at least another anode to the long-sized substrate.

(4) The three or more anodes have larger surface areas as arranged closer to the center.

In this case, the currents flowing from the plurality of anodes to the long-sized substrate can be equal or close to one another. Accordingly, efficiency of the plating performed on the long-sized substrate can be more sufficiently improved while plating burn is prevented.

(5) According to another aspect of the present invention, a method of manufacturing a printed circuit board includes the steps of preparing a long-sized substrate, and performing electrolytic plating on the long-sized substrate, wherein the step of performing the electrolytic plating includes the steps of transporting the long-sized substrate in a length direction of the long-sized substrate through a plating solution container that contains a plating solution, and applying a voltage between the long-sized substrate and three or more anodes placed in the plating solution container to line up along the long-sized substrate that is transported, and a surface area of each of the anodes, which are arranged at both ends, of the three or more anodes is smaller than a surface area of at least another anode.

In the method of manufacturing the printed circuit board, the long-sized substrate is transported in the length direction by the transporting unit through the plating solution container that contains the plating solution. The three or more anodes are placed in the plating solution container to line up along the direction in which the long-sized substrate is transported. In this state, the voltage is applied between the plurality of anodes and the long-sized substrate by the power feeding unit such that the long-sized substrate acts as a cathode, thereby subjecting the long-sized substrate to the electrolytic plating.

In this case, since the surface area of each of the anodes arranged at the both ends of the plurality of anodes is set smaller than the surface area of the at least another anode, a resistance value of each of the anodes arranged at the both ends is larger than a resistance value of the at least another anode. This suppresses currents flowing from the anodes at the both ends to the long-sized substrate. Thus, each of the currents flowing from the anodes at the both ends to the long-sized substrate can be equal or close to a current flowing from the at least another anode to the long-sized substrate. Accordingly, current density at each of the portions of the long-sized substrate that are opposite to the anodes at the both ends can be equal or close to current density of the portion of the long-sized substrate that is opposite to the at least another anode. In this case, constant currents supplied to the plurality of anodes are increased, thereby allowing the currents flowing from the anodes at the both ends to the long-sized substrate and the current flowing from the at least another anode to the long-sized substrate to be close to an upper limit of the current at which plating burn does not occur. Thus, efficiency of the plating performed on the long-sized substrate can be improved while plating burn is prevented. As a result, the printed circuit board can be satisfactorily and efficiently manufactured.

According to the present invention, the currents flowing from the anodes at the both ends to the long-sized substrate and the current flowing from the at least another anode to the long-sized substrate can be brought close to the upper limit of the current at which plating burn does not occur. Thus, efficiency of the plating performed on the long-sized substrate can be improved while plating burn is prevented.

Other features, elements, characteristics, and advantages of the present invention will become more apparent from the following description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a plating apparatus according to an embodiment of the present invention;

FIG. 2 is a diagram showing anodes of the plating apparatus of FIG. 1;

FIG. 3 shows schematic sectional views for use in illustrating steps in one example of a method of manufacturing a printed circuit board using the plating apparatus according to the present embodiment;

FIG. 4 is a diagram showing the configurations of anodes of a plating apparatus according to a second embodiment;

FIG. 5 is a diagram showing currents flowing through the anodes in an inventive example 1;

FIG. 6 is a diagram showing currents flowing through the anodes in a comparative example 1; and

FIG. 7 is a diagram showing currents flowing through the anodes in inventive examples 2, 3 and a comparative example 2.

DETAILED DESCRIPTION OF THE INVENTION

Description will be made of a plating apparatus and a method of manufacturing a printed circuit board according to one embodiment of the present invention while referring to the drawings.

(1) First Embodiment

(1-1) Configuration of Plating Apparatus

FIG. 1 is a schematic perspective view of a plating apparatus 100 according to a first embodiment. As shown in FIG. 1, the plating apparatus 100 includes a box-shaped plating tank 102. The plating tank 102 has a bottom surface and four side surfaces. Two side surfaces of the plating tank 102 that are opposite to each other have long-sized openings 103, respectively, which extend in a vertical direction.

A pair of transport rollers 101 a, 101 b extending in the vertical direction is rotatably provided to close one opening 103, and a pair of transport rollers 101 c, 101 d extending in the vertical direction is rotatably provided to close the other opening 103. In this case, the transport rollers 101 a to 101 d seal the two openings 103 in a liquid-tight manner.

A plating solution including copper sulfate, for example, is contained in the plating tank 102. When the plating solution contains insufficient copper ions, powdered copper oxide may be added to the plating solution. A storing tank (not shown) that receives the plating solution leaking out of the plating tank 102 may be arranged below the plating tank 102. In the case, the plating solution accumulating in the storing tank is returned to the plating tank 102 by a pump.

A long-sized substrate 10 is sandwitched between the pair of transport rollers 101 a, 101 b and between the pair of transport rollers 101 c, 101 d. The transport rollers 101 a to 101 d rotate, thereby causing the long-sized substrate 10 to pass through the inside of the plating tank 102 and to be transported in a direction indicated by an arrow MD (hereinafter referred to as a transport direction). Accordingly, the long-sized substrate 10 is successively immersed in the plating solution in the plating tank 102.

A power feed roller 50 a is provided in an upstream position of the transport rollers 101 a, 101 b in the transport direction of the long-sized substrate 10 while being rotatable around its axis in the vertical direction. A power feed roller 50 b is provided in a downstream position of the transport rollers 101 c, 101 d in the transport direction of the long-sized substrate 10 while being rotatable around its axis in the vertical direction.

The power feed rollers 50 a, 50 b rotate while being in contact with one surface of the long-sized substrate 10. A plating region to be subjected to electrolytic plating is provided on the one surface of the long-sized substrate 10. The power feed rollers 50 a, 50 b are in contact with the one surface of the long-sized substrate 10, so that each of the power feed rollers 50 a, 50 b is electrically connected to the plating region of the long-sized substrate 10. The power feed rollers 50 a, 50 b are each connected to a negative electrode of a rectifier 42. The rectifier 42 is connected to an AC power supply (not shown).

Three or more (six in this example) bar-shaped anodes 1 are provided in the plating tank 102 to line up along the long-sized substrate 10. In this case, the plurality of anodes 1 are arranged to be opposite and close to the one surface (surface on which the plating region is provided) of the long-sized substrate 10. Titanium bars coated with iridium oxide are used as the anodes 31, for example. The plurality of anodes 1 are each connected to a positive electrode of the rectifier 42 in parallel with one another.

Via the rectifier 42, a voltage is applied between the plurality of anodes 1 and the plating region of the long-sized substrate 10 connected to the power feed rollers 50 a, 50 b. In this case, the plating region of the long-sized substrate 10 acts as a cathode in the plating tank 102. Accordingly, the plating region of the long-sized substrate 10 is subjected to the electrolytic plating (copper plating).

The rectifier 42 includes a constant current controlling circuit, which controls currents supplied from the rectifier 42 to the plurality of anodes 1 (hereinafter referred to as supplied currents) to be constant.

Here, the surface area of each of the anodes 1, which are arranged at both ends, of the plurality of anodes 1 is smaller than the surface area of at least another anode 1 in the present embodiment. Description will be made of the surface area of each of the anodes 1 in the following paragraphs.

(1-2) The Surface Areas of the Anodes

FIG. 2 is an enlarged view of the plurality of anodes 1 of the plating apparatus 100 according to the present embodiment. Among the plurality of anodes 1, two anodes 1 arranged at the both ends are referred to as both end anodes 1, two anodes 1 adjacent to the two both end anodes 1, respectively, are referred to as intermediate anodes 1, and two anodes 1 arranged between the two intermediate anodes 1 are referred to as center anodes 1 in the following description. The area of the cross section, which is perpendicular to a length direction, of each anode 1 is referred to as the cross sectional area of each anode 1.

As shown in FIG. 2, the two both end anodes 1 have the same shape, the two intermediate anodes 1 have the same shape, and the two center anodes 1 have the same shape in the present embodiment. The both end anodes 1, the intermediate anodes 1 and the center anodes 1 have the equal length in the vertical direction. The cross sectional area of each of the both end anodes 1 is smaller than the cross sectional area of each of the intermediate anodes 1, and the cross sectional area of each of the intermediate anodes 1 is smaller than the cross sectional area of each of the center anodes 1.

Therefore, the surface area of each of the both end anodes 1 is smaller than the surface area of each of the intermediate anodes 1, and the surface area of each of the intermediate anodes 1 is smaller than the surface area of each of the center anodes 1. The surface area of each of the both end anodes 1 is not less than 300 cm² and not more than 900 cm², the surface area of each of the intermediate anodes 1 is not less than 500 cm² and not more than 1500 cm², and the surface area of each of the center anodes 1 is not less than 1000 cm² and not more than 2000 cm², for example. The ratio of the surface area of the both end anode 1 to the surface area of the center anode 1 is not less than 30% and not more than 50%, and the ratio of the surface area of the intermediate anode 1 to the surface area of the center anode 1 is not less than 50% and not more than 70%, for example.

Accordingly, a resistance value of the both end anode 1 is larger than a resistance value of the intermediate anode 1, and the resistance value of the intermediate anode 1 is larger than a resistance value of the center anode 1.

It is preferable that the length of each anode 1 in the vertical direction is not less than 100 mm and not more than 500 mm, the length of each anode 1 in the transport direction of the long-sized substrate 10 is not less than 20 mm and not more than 150 mm, and the length of each anode 1 in a direction perpendicular to the long-sized substrate 10 is not less than 20 mm and not more than 80 mm, for example.

(1-3) Method of Manufacturing Printed Circuit Board

FIG. 3 shows schematic sectional views for use in illustrating steps in one example of a method of manufacturing a printed circuit board using the plating apparatus according to the present embodiment.

First, a long-sized insulating layer 20 made of polyimide, for example, is prepared as shown in FIG. 3 (a). Next, a seed layer 21 made of nickel-chromium, for example, is formed by nonelectrolytic plating or sputtering on the insulating layer 20 as shown in FIG. 3 (b). Then, a dry film or the like is laminated on the seed layer 21, followed by exposure and development, thereby forming a plating resist 22 having an inverted pattern of a wiring pattern, which is formed in the following step as shown in FIG. 3 (c). In this manner, the long-sized substrate 10 (FIG. 1) is formed.

The long-sized substrate 10 is then subjected to the electrolytic plating by the plating apparatus 100 of FIG. 1 in the above-described manner, so that a wiring layer 23 made of copper, for example, is formed on a portion of the seed layer 21 not having the plating resist 22 formed thereon as shown in FIG. 3 (d). In this case, the portion of the seed layer 21 not having the plating resist 22 formed thereon corresponds to the foregoing plating region.

After the plating resist 22 is removed by way of stripping or the like, the seed layer 21 excluding its region below the wiring layer 23 is removed using an etching solution as shown in FIG. 3 (e). Accordingly, the printed circuit board 25, in which a wiring pattern 24 composed of the seed layer 21 and the wiring layer 23 is formed on the insulating layer 20, is formed.

(1-4) Effects

The experiments and study conducted by the inventor show that when constant currents are supplied to the plurality of anodes 1 arranged along the long-sized substrate 10, each of currents flowing from the anodes 1 at the both ends to the long-sized substrate 10 tends to be larger than each of currents flowing from the other anodes 1 to the long-sized substrate 10. Therefore, current density at each of portions of the long-sized substrate 10 that are opposite to the anodes 1 at the both ends is larger than current density of each of portions of the long-sized substrate 10 that are opposite to the other anodes 1.

In the plating apparatus 100 according to the first embodiment, the surface area of each of the both end anodes 1 of the plurality of anodes 1 is smaller than the surface area of each of the other anodes 1. In this case, the resistance value of each of the both end anodes 1 is larger than the resistance value of each of the other anodes 1.

This suppresses the currents flowing from the both end anodes 1 to the long-sized substrate 10. Thus, each of the currents flowing from the both end anodes 1 to the long-sized substrate 10 can be equal or close to each of the currents flowing from the other anodes 1 to the long-sized substrate 10. Accordingly, the current density at each of the portions of the long-sized substrate 10 that are opposite to the both end anodes 1 can be equal or close to the current density of each of the portions of the long-sized substrate 10 that are opposite to the other anodes 1.

In this case, the constant currents (supplied currents) supplied to the plurality of anodes 1 are increased, thereby allowing the currents flowing from the both end anodes 1 to the long-sized substrate 10 and the currents flowing from the other anode 1 to the long-sized substrate 10 to be close to an upper limit of the current at which plating burn does not occur. As a result, efficiency of the plating performed on the long-sized substrate 10 can be improved while plating burn is prevented.

The plurality of anodes 1 are each formed of a metal bar in the plating apparatus 100 of the present embodiment. Therefore, the area of the cross section, which is perpendicular to the length direction, of the anode 1 formed of the metal bar is adjusted in manufacture of each anode 1, so that the surface area of each anode 1 can be accurately adjusted. Accordingly, each of the currents flowing from the both end anodes 1 to the long-sized substrate 1 can be accurately equal or close to each of the currents flowing from the other anodes 1 to the long-sized substrate 10.

In the plating apparatus 100 according to the present embodiment, the surface areas of the plurality of anodes 1 are set gradually larger from the both end anodes 1 to the center anodes 1. This allows the currents flowing from all the anodes 1 to the long-sized substrate 10 to be more accurately equal or close to one another. Accordingly, efficiency of the plating performed on the long-sized substrate 10 can be more sufficiently improved while plating burn is prevented.

If the currents flowing from the plurality of anodes 1 to the long-sized substrate 10 can be equal or close to one another, the surface area of each of the intermediate anodes 1 may be equal to or smaller than the surface area of each of the center anodes 1.

The two both end anodes 1 may have different shapes, the two intermediate anodes 1 may have different shapes, and the two center anodes 1 may have different shapes.

(2) Second Embodiment

Description will be made of a plating apparatus 100 according to a second embodiment of the present invention by referring to differences from the plating apparatus 100 of the first embodiment.

FIG. 4 is a diagram showing the configurations of a plurality of anodes 2 of the plating apparatus 100 according to the second embodiment. As shown in FIG. 4, the plating apparatus 100 according to the second embodiment includes three or more (six in this example) anodes 2 instead of the three or more anodes 1. Each anode 2 has such a configuration that a plurality of spherical anode balls 112 made of copper are accommodated in a mesh case 110 made of titanium, for example. Each anode 2 is arranged within the plating tank 102 while being accommodated in an acid-resistant anode bag 113.

In the following description, two anodes 2, which are arranged at both ends, of the plurality of anodes 2 are referred to as both end anodes 2, two anodes 2 adjacent to the two both end anodes 2 are referred to as intermediate anodes 2, and two anodes 2 arranged between the two intermediate anodes 2 are referred to as center anodes 2.

In the plating apparatus 100 according to the present embodiment, the two both end anodes 2 have the same number of anode balls 112, the two intermediate anodes 2 have the same number of anode balls 112, and the two center anodes 2 have the same number of anode balls 112. The number of anode balls 112 in each of the both end anodes 2 is smaller than the number of anode balls 112 in each of the intermediate anodes 2, and the number of anode balls 112 in each of the intermediate anodes 2 is smaller than the number of anode balls 112 in each of the center anodes 2.

The number of anode balls 112 in each anode 2 corresponds to the surface area of each anode 2. That is, the anode 2 having the larger number of anode balls 112 has the larger surface area. Therefore, the surface area of each of the both end anodes 2 is smaller than the surface area of each of the intermediate anodes 2, and the surface area of each of the intermediate anodes 2 is smaller than the surface area of each of the center anodes 2. When the anode balls 112 each having the diameter of 27 mm, for example, are employed, the both end anodes 2 each have not less than 10 and not more than 40 anode balls 112, the intermediate anodes 2 each have not less than 30 and not more than 80 anode balls 112, and the center anodes 2 each have not less than 60 and not more than 120 anode balls 112, for example.

In the plating apparatus 100 according to the second embodiment, the number of anode balls 112 in each of the both end anodes 2 of the plurality of anodes 2 is smaller than the number of anode balls 112 in each of the other anodes 2. In this case, a resistance value of each of the both end anodes 2 is larger than a resistance value of each of the other anodes 2.

This suppresses currents flowing from the both end anodes 2 to the long-sized substrate 10. Accordingly, each of the currents flowing from the both end anodes 2 to the long-sized substrate 10 can be equal or close to each of currents flowing from the other anodes 2 to the long-sized substrate 10. This allows current density of each of portions of the long-sized substrate 10 that are opposite to the both end anodes 2 to be equal or close to current density of each of portions of the long-sized substrate 10 that are opposite to the other anodes 2.

In this case, the constant currents (supplied currents) supplied to the plurality of anodes 2 are increased, thereby allowing the currents flowing from the both end anodes 2 to the long-sized substrate 10 and the currents flowing from the other anodes 1 to the long-sized substrate 10 to be close to the upper limit of the current at which plating burn does not occur. As a result, efficiency of the plating performed on the long-sized substrate 10 can be improved while plating burn is prevented.

The plurality of anodes 2 are each composed of the case 110 and the anode balls 112 accommodated in the case 110 in the plating apparatus 100 of the present embodiment. Therefore, the surface area of each anode 2 can be easily adjusted by adjusting the number of anode balls 112 in each anode 2. This allows each of the currents flowing from the both end anodes 2 to the long-sized substrate 10 to be easily equal or close to each of the currents flowing from the other anodes 2 to the long-sized substrate 10.

The diameter of each of the anode balls 112 is not less than 10 mm and not more than 30 mm, for example. The length of each of the cases 110 in the vertical direction is not less than 100 mm and not more than 500 mm, the length of each of the cases 110 in the transport direction of the long-sized substrate 10 is not less than 20 mm and not more than 150 mm, and the length of each of the cases 110 in the direction perpendicular to the long-sized substrate 10 is not less than 20 mm and not more than 80 mm, for example.

The two both end anodes 2 may have different numbers of anode balls 112, the two intermediate anodes 2 may have different numbers of anode balls 112, and the two center anodes 2 may have different numbers of anode balls 112 if the currents flowing from the plurality of anodes 2 to the long-sized substrate 10 can be equal or close to one another.

The cases 110 of the plurality of anodes 2 may have the same shape or different shapes. Note that it is preferable that the plurality of anode balls 112 are arranged at equal spacings in the vertical direction in the plurality of anodes 2.

(3) Modifications

While the six anodes 1, 2 are provided in the plating tank 102 in the first and second embodiments, the present invention is not limited to this. Three to five, or seven or more anodes 1, 2 may be provided in the plating tank 102.

In the case, the surface area of each of the anodes 1, 2 at the both ends is set smaller than the surface area of at least another anode 1, 2. In addition, it is preferable to set the surface areas to gradually increase from the anodes 1, 2 at both ends to the anodes 1, 2 at the center.

(4) Inventive Examples and Comparative Examples

The long-sized substrate 10 was subjected to the electrolytic plating by the plating apparatus 100 under various conditions, and the currents flowing through the anodes were measured.

(4-1) Inventive Example 1

The plating apparatus 100 according to the first embodiment was used in an inventive example 1. The surface area of each of the both end anodes 1 was 450 cm², the surface area of each of the intermediate anodes 1 was 750 cm², and the surface area of each of the center anodes 1 was 1500 cm². In this case, the ratio of the surface area of the both end anode 1 to the surface area of the center anode 1 was 30%, and the ratio of the surface area of the intermediate anode 1 to the surface area of the center anode 1 was 50%.

(4-2) Inventive Examples 2 and 3

The plating apparatus 100 according to the second embodiment was used in inventive examples 2 and 3. The anode balls 112 each having the diameter of 27 mm were used in the inventive example 2. The number of anode balls 112 in each of the both end anodes 2 was 25, the number of anode balls 112 in each of the intermediate anodes 2 was 45, and the number of anode balls 112 in each of the center anodes 2 was 80. In the inventive example 3, the anode balls 112 each having the diameter of 27 mm were used. The number of anode balls 112 in each of the both end anodes 2 was 25, the number of anode balls 112 in the upstream intermediate anode 2 in the transport direction of the long-sized substrate 10 was 45, the number of anode balls 112 in the downstream intermediate anode 2 in the transport direction of the long-sized substrate 10 was 50, and the number of anode balls 112 in each of the center anodes 2 was 80.

(4-3) Comparative Example 1

A plating apparatus 100 having the same configuration as the plating apparatus 100 of the inventive example 1 except that all the six anodes 1 each have the surface area of 1500 cm² was used in a comparative example 1.

(4-4) Comparative Example 2

A plating apparatus 100 having the same configuration as the plating apparatus 100 of each of the inventive examples 2, 3 except that the number of anode balls 112 was 80 in each of the six anodes 2 was used in a comparative example 2.

(4-5) Evaluations of the Inventive Example 1 and the Comparative Example 1

The constant currents (supplied currents) flowing from the rectifier 42 to the plurality of anodes 1 were adjusted to 30A, 45A and 60A, and the currents flowing through the anodes 1 were examined in the inventive example 1 and the comparative example 1. FIG. 5 shows the currents flowing through the anodes 1 in the inventive example 1. FIG. 6 shows the currents flowing through the anodes 1 in the comparative example 1.

In FIGS. 5 and 6, the abscissa represents the position of each anode 1 in the transport direction (direction indicated by the arrow MD) of the long-sized substrate 10, and the ordinate represents the current [A] flowing through each anode 1.

As shown in FIG. 5, the currents flowing through the six anodes 1 were substantially uniform in any of cases where the supplied currents were 30A, 45A and 60A in the inventive example 1. On the other hand, as shown in FIG. 6, each of the currents flowing through the both end anodes 1 was larger than each of the currents flowing through the center anodes 1 and the intermediate anodes 1 in any of the cases where the supplied currents were 30A, 45A and 60A in the comparative example 1. That is, the currents flowing through the six anodes 1 were nonuniform.

(4-6) Evaluations of the Inventive Examples 2, 3 and the Comparative Example 2

In the inventive examples 2, 3 and the comparative example 2, the constant currents (supplied currents) flowing from the rectifier 42 to the plurality of anodes 2 were adjusted to 45A, and the currents flowing through the anodes 2 were examined. FIG. 7 shows the currents flowing through the anodes 2 in the inventive examples 2, 3 and the comparative example 2.

In FIG. 7, the abscissa represents the position of each anode 2 in the transport direction (direction indicated by the arrow MD) of the long-sized substrate 10, and the ordinate represents the current [A] flowing through each anode 2.

As shown in FIG. 7, the currents flowing through the six anodes 2 were substantially uniform in the inventive examples 2 and 3. On the other hand, each of the currents flowing through the both end anodes 2 was larger than each of the currents flowing through the center anodes 2 and the intermediate anodes 2 in the comparative example 2. That is, the currents flowing through the six anodes 2 were nonuniform.

It was found as a result that the surface area of each of the anodes 1, 2, which were arranged at the both ends, of the plurality of anodes 1, 2 was set smaller than the surface area of each of the other anodes 1, 2, so that each of the currents flowing from the both end anodes 1, 2 to the long-sized substrate 10 can be equal or close to each of the currents flowing from the other anodes 1, 2 to the long-sized substrate 10.

Accordingly, the currents flowing from the anodes 1, 2 at the both ends to the long-sized substrate 10 and the currents flowing from the other anodes 1, 2 to the long-sized substrate 10 can be brought close to the upper limit of the current at which plating burn does not occur by increasing the supplied currents to the plurality of anodes 1, 2.

(5) Correspondences between Elements in the Claims and Parts in Embodiments

In the following paragraphs, non-limiting examples of correspondences between various elements recited in the claims below and those described above with respect to various preferred embodiments of the present invention are explained.

In the above-described embodiments, the long-sized substrate 10 is an example of a long-sized substrate, the plating apparatus 100 is an example of a plating apparatus, the plating tank 102 is an example of a plating solution container, the transport rollers 101 a to 1001 d are examples of a transporting unit, the rectifier 42 and the power feeding rollers 50 a, 50 b are an example of a power feeding unit, the anode 1, 2 is an example of an anode, the anode 1 is an example of a metal bar, the anode ball 112 is an example of a metal ball, the case 110 is an example of a case, and the printed circuit board 25 is an example of a printed circuit board.

As each of various elements recited in the claims, various other elements having configurations or functions described in the claims can be also used.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A plating apparatus arranged to perform plating on a long-sized substrate, comprising: a plating solution container arranged to contain a plating solution; a transporting unit arranged to transport said long-sized substrate in a length direction of said long-sized substrate through said plating solution container; three or more anodes placed in said plating solution container to line up along said long-sized substrate transported by said transporting unit; and a power feeding unit arranged to apply a voltage between said long-sized substrate and said three or more anodes such that said long-sized substrate acts as a cathode, wherein a surface area of each of the anodes, which are arranged at both ends, of said three or more anodes is smaller than a surface area of at least another anode.
 2. The plating apparatus according to claim 1, wherein each of said three or more anodes is composed of a metal bar, and an area of the cross section of each of the anodes arranged at said both ends is smaller than an area of the cross section of the at least another anode, and said cross sections of said anodes are perpendicular to a length direction of said anodes.
 3. The plating apparatus according to claim 1, wherein each of said three or more anodes includes: a plurality of metal balls; and a case in which said plurality of metal balls are accommodated, and the number of said metal balls in each of the anodes, which are arranged at said both ends, of said three or more anodes is smaller than the number of said metal balls in the at least another anode.
 4. The plating apparatus according to claim 1, wherein said three or more anodes have larger surface areas as arranged closer to the center.
 5. A method of manufacturing a printed circuit board comprising the steps of: preparing a long-sized substrate; and performing electrolytic plating on said long-sized substrate, wherein said step of performing the electrolytic plating includes the steps of: transporting said long-sized substrate in a length direction of said long-sized substrate through a plating solution container that contains a plating solution; and applying a voltage between said long-sized substrate and three or more anodes placed in said plating solution container to line up along said long-sized substrate that is transported; and a surface area of each of the anodes, which are arranged at both ends, of said three or more anodes is smaller than a surface area of at least another anode. 